The invention relates to vacuum chucks for holding workpieces, and more particularly to vacuum chucks capable of holding multiple workpieces, especially microelectronic circuit package substrates, precisely in position despite repeated application of severe lateral forces to the workpieces.
Previously, die bonding or wire bonding of hybrid integrated circuits has usually involved performing all required die bonding or wire bonding operations on one single hybrid package substrate at a time. In some instances, wherein mechanical clamps have been utilized to attach the hybrid substrate to an X/Y table or chuck, for example, in an automated wire bonding or die bonding machine, excessive amounts of time have been required for loading and unloading the hybrid package substrates. For example, when vacuum chucks have been used to hold the hybrid package substrate against the surface of the vacuum chuck, there has been a problem in preventing minute amounts of cummulative lateral displacement of the hybrid package substrate as the X/Y chuck automatically moves the package substrate from one bonding location to another to successively align different bonding pads on the package substrate or an integrated circuit chip thereon with a wire bonding head of a wire bonding machine. The X/Y chucks are controlled by servomechanisms which rapidly move the X/Y chuck from one bonding location to another, and thereby subject the hybrid substrate to severe repetitive lateral forces, each time causing a small amount of lateral displacement of the package substrate relative to the chuck. For example, Hughes Aircraft Company, Industrial Products Division of Carlsbad, Calif., has recently manufactured very sophisticated wire bonding machines and die bonding machines. These machines include an X/Y table or base to which a package holding fixture or chuck can be attached, a die bonding head or wire bonding head, a TV camera, a TV monitor, a microscrope lens through which the TV camera can monitor the hybrid package substrate or integrated circuit die presently being bonded, and a computer which stores an operating program and data that determines the precise location of the X/Y table for each bonding operation on each hybrid package substrate. These automatic bonding machines would be ideally suited to automatic die bonding and automatic wire bonding of many hybrid integrated circuits on a single vacuum chuck if such a chuck were available. It would be highly desirable if the chuck could be very rapidly loaded and unloaded. It is imperative that every hybrid package be held very securely in fixed relationship to the chuck and avoid even minute amount of lateral displacement due to forces produced on the hybrid substrate or any integrated circuit die thereon by bonding and/or acceleration and decceleration forces as the X/Y table rapidly and abruptly moves from one bonding location to another.
Although various vacuum chucks have been used in the integrated circuit industry for years, such as the one shown in U.S. Pat. No. 3,617,045 by Da Costa et al., none of the prior vacuum chucks devices have overcome the above described problems. Although various vacuum sealing techniques have been used in conjunction with holding workpieces in place, to our knowledge no vacuum chuck has been provided, either in conjunction with integrated circuit bonding equipment or other applications, which overcomes the above-mentioned problems and permits low cost, rapid loading of multiple hybrid integrated circuit package substrates on a bonding machine and allows automatic, very rapid alignment of hundreds of locations on each package substrate with a bonding head and avoids essentially all lateral displacement of the package substrate due to the repetitive acceleration and decceleration forces. The above U.S. Pat. Nos. 3,617,045 and 3,580,460, 4,039,114, 3,409,977, and 3,973,713 are generally indicative of the state of the art.
Therefore, there is a need for a technique and apparatus for holding a workpiece securely and very precisely in a vacuum chuck despite numerous repetitive procedures which subject the workpiece to lateral acceleration and decceleration forces.